documentation changes: updated Changelog and NEWS, wrote sections on
pipes and updated the Performance section; updated timings.sc with
gforth-0.5.9 numbers
Changed name in bootmessage from GForth to Gforth.

On platforms that support the SA_SIGINFO flag (Linux is not quite
there yet), there are now new signal handlers that perform more
precise error reporting (in particular for SIGFPE and SIGSEGV).
Minor fixes.

New "docclean" target for makefile (removes glossary dependencies when
rebuilding documentation). Changes to .fs files and prim are restricted
to glossary (\G) additions for the documentation; this has necessitated
the addition of new white-space in places to stop the \G stuff from
obscuring the code. Many additions to doc/gforth.ds - new sections
added, a few things moved and some sections re-written slightly. There
are a set of things to tidy up before this rev. is suitable for
release, and those will be my highest priority. I have also used
"@comment TODO" to highlight other sections I plan to work on, and
added a set of comments at the start to indicate other things I plan
to modify in the medium-term.